In situ reflectance-difference spectroscopy of doped CdTe and ZnTe grown by molecular beam epitaxy

We have used reflectance-difference (RD) spectroscopy (UV-visible energy range) during the growth and doping process of CdTe(001) and ZnTe(001) layers by molecular beam epitaxy (MBE). The MBE chamber is equipped with an electron cyclotron resonance cell to generate N plasma and a $ZnCl2$ effusion cell for the p- and n-type doping, respectively. After the first stages of the growth and prior doping, different spectral features were found as we changed from Cd or Zn to Te stabilized conditions due to surface anisotropy. However, as the doping of the growing layer further increased, the RD spectra of both surfaces showed resonances around $E1$ and $E1+Δ1$ interband transitions due to the linear electro optic (LEO) effect. Although RD spectra exhibit similar line shapes dominated by surface transitions, differences due to the LEO can be isolated. Different Fermi level pinning mechanisms are proposed for both materials because the RD measurements of the LEO strongly depend on surface termination.